We will be providing more information about the ATF soon.
ATF Form 7, Application for License may be obtained from the Firearms and Explosives Licensing Center in Atlanta, Goergia 1-404-417-2750, or your local ATF office.
For over .500" bore cartridges and rifles there are a few simple steps to take. I have personally completed these steps for the 550 Express, 550 Magnum, 550 Magnum Long, and the 550 RNS. I have also completed the steps for the first .550" caliber hunting rifle and all experiences with the ATF have been some of the most professional people I have delt with.
To recieve a sporting exemption on a sporting cartridge that exceeds the .500" bore diameter write to the FTAB(Firearms Technology Branch), 244 Nerdy Road, Martinsburg, WV 25401. Include a case drawing and a leter requesting a sporting exemption based on the type of firearm the sporting cartridge will be fired in (bolt action, single shot, double rifle) and that the cartridge is for hunting/sporting.
I also recieved a non destructive device exemption for the first 550 Magnum rifle by again writing to the FATB clearing stating that the rifle I intend too build will be for sporting use only. I included several photos of rifle which illustrated how my rifle would be built. I did have to send in my barreled action for examination and here is the official response.
"The FTB evaluation, which is intended to determine the exemption status of your submitted sample, sn xxxxx, chambered in 550 Magnum caliber, has found that this rifle is designed solely for sporting purposes and that it is not a destructive device subject to all the provisions of the NFA. Further, a rifle of such caliber would not be a "destructive device" as defined in the Gun Control Act of 1968, 18 U.S.C. 921(a)(4). The gunsmith building this weapon, sn xxxxx, chambered in 550 Magnum caliber, does not have to be licensed as a Manufacturer of destructive devices."